Mechanical Technology August 2015

⎪ Proactive maintenance, lubrication and contamination management ⎪

Refurbishment of the Transnet trac- tion motor casings can be done with the with field coils intact and the change in coating area around the profile (left) is easily accommodated by the process.

After starting the process manually, the plating is mechanised by attaching the two plating shoes to a rotating beam. The total electrical energy in kWh is used to determine the coating thickness for a given area to a thickness accuracy of better than 99%.

volume, so it can be used to determine the coating thick- ness for a given area. “We have developed plat- ing characteristic data for all of our electrolytes and, for any given application, these can be used to determine the quantity of electrolyte required, the plating current and voltage and the total

damage will be cut away before a new section is welded on. This has potential consequences with respect to distortion and may potentially affect the current carrying capacity. “Using our cold selective electroplat- ing process, however, we can take all of the necessary equipment onto site and complete the repair in situ . Without dismantling anything at all, we will build up the damaged aluminium section and we can then coat the surface with silver. I am certain that we can do this job at a fraction of the cost of sending the whole component out for a traditional repair,” Pienaar reveals. The equipment needed is relatively simple: a dc rectifier; the anode ap- plicator with its copper shoe and felt covering; a solution tray to capture and recycle electrolyte; a small variable flow pump to recirculate the electrolyte; and the electrolytic solution itself. For coating circular components, it is also possible to automate the process to some extent, by rotating either the component or the shoe so as to maintain brush-like contact. The plating control unit is equipped with an amp-hour meter with a six-digit impulse counter to ensure precise plat- ing deposits. Pienaar explains: “The deposition rate for this process is directly proportional to the current density. This is because there is an exact relationship between the number of electrons flowing into the cathode and the amount of metal deposited. The total electrical energy in kWh therefore relates directly to deposit

The journal-bearing surface of a shaft coated with a nickel cobalt hardened layer.

casings, with field coils intact, it costs something like R100 000 for a strip out and repair using fusion-based processes. We are able to avoid having to remove the coil while repairing the casing and journal bearing bores, completing the equivalent job at a fraction of the cost,” he says. Of the six main Transnet workshops: Koedoespoort, Bloemfontein, Durban, Germiston, Salt River and Uitenhage all have invested in their own selective electroplating equipment. “We have equipped these Transnet facilities with the rectifier and rotating equipment required and we supply the electrolytes for them to refurbish all of their rail axles for themselves. “We see this as an ideal model to take to other industries in South Africa. Whether as part of small engineering shops or as mobile service providers op- erating onsite or out of containers, we see this process as an ideal entrepreneurial opportunity. As well as reducing main- tenance costs for industry, the process can help to create jobs and improve the economy,” Pienaar concludes. q

energy required to achieve the neces- sary thickness. On a 100 µ m thickness, we will be accurate to within 0.01  µ m or within 99% of the specification,” he assures, adding that no post finishing is required once the process is completed. “The finished surface does not look as bright as those coated in an electroplating tank, but measurements show that the selective electroplating process produces higher surface smoothness than tradi- tional electroplating.” In addition, all the electrolytes are manufactured in South Africa and the intellectual property associated with the characteristic data is South African owned. “But the idea is not to sit on this technology as an exclusive service pro- vider. We aim to help small businesses to set up local selective electroplating and refurbishing services all over the country,” Pienaar continues. “Cash flows in current times are being squeezed and we believe that greater access to this process can save clients significant amounts of money in the long term. “On the Transnet traction motor

Mechanical Technology — August 2015

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